London: Debate over the merits of video assistant refereeing was again raised as a Romelu Lukaku double eased Manchester United into the FA Cup quarter-finals in a 2-0 win at Huddersfield despite a controversial call going against Jose Mourinho's men.

Juan Mata thought he had put United into a 2-0 lead just before half-time only for the Spaniard's effort to be ruled out by the video referee after a lengthy delay, and without conclusive proof the officials on the field had made the wrong decision.

Thankfully for United, and the authorities, that decision didn't have a definitive influence on the outcome as Lukaku struck early in both halves to take his tally for the season to 21.

"If they have the VAR to help them make the right decisions, I think the referees will be happy with that," said Mourinho.

"But if the VAR change their good decisions for bad decisions, I think they are not happy with that."

United will face Brighton in the last eight, with Chelsea travelling to Leicester as four of the Premier League's top five were kept apart in the quarter-final draw.

Manchester City will host Southampton if they see off third-tier Wigan on Monday, and Tottenham face a trip to Sheffield Wednesday or Swansea should they progress in Sunday's visit to Rochdale.

United were without Paul Pogba due to illness as a frustrating few weeks for the Frenchman continued after a dramatic dip in form that has seen him hauled off by Mourinho in recent defeats at Tottenham and Newcastle.

Mourinho made six changes in all from last weekend's shock reverse at St. James' Park, but his decision to retain Lukaku paid dividends when the Belgian burst onto Mata's pass to open the scoring inside three minutes.

Mata then had the ball in the net himself a minute before the break. A delay in referring the decision was exacerbated as the lines used to help the video official decipher offside decisions appeared to be far from straight.

"I'm up for it and I think it is needed, especially when it is a clear decision," said Mata.

"Hopefully it will be quicker as well, but I think it will be good for football to be a bit more fair."

United were left to mull over their grievance at half-time, but quickly ensured it wasn't to cost them too dearly as a brilliant one-two between Lukaku and Alexis Sanchez freed the former to slot low past Jonas Lossl.

More West Brom woe

Elsewhere, a week to forget for West Brom was rounded off with an FA Cup exit as fellow Premier League strugglers Southampton won 2-1 at the Hawthorns.

West Brom boss Alan Pardew named Jonny Evans and Gareth Barry in his starting line-up despite the experienced duo forming half of a group of four players questioned by Spanish police this week over the theft of a taxi on the club's warm-weather training trip to Barcelona.

"There was a problem in terms of selection because of the incident to go with my strongest team," said Pardew.

"I decided to do that. I felt I needed to make a little bit of a statement about the events. I was far from happy over them and made Gareth (McAuley) captain today."

Wesley Hoedt took advantage of some slack West Brom marking to head home his first goal for Southampton just 11 minutes in.

Dusan Tadic doubled the visitors' advantage on the counter-attack after the break and Southampton held out despite Salomon Rondon's spectacular volley pulling a goal back.

Brighton cruised into the last eight as fourth-tier Coventry City's fairytale run came to a crashing end in a 3-1 defeat.

Sheffield Wednesday and Swansea City face an unwanted replay after an insipid 0-0 draw on Swansea boss Carlos Carvalhal's return to Hillsborough.

"It's a score nobody wants," said Carvalhal, whose side are also battling for Premier League survival.

"Maybe in the future, if the managers and referee agree after the first game we can go to penalties, we can finish the game today."